1. Technical Field
The present invention relates to a complex antenna device, and more particularly, to a complex antenna device in which a planar antenna and a bar antenna are combined.
2. Related Art
Currently, as known in this technical field, various antennas are mounted on a vehicle such as an automobile. As such an antenna, for example, an antenna for a GPS (Global Positioning System), an antenna for an SDARS (satellite digital audio radio service), an antenna for a radio telephone, or an antenna for AM/FM radio is used.
The GPS (Global Positioning System) is a satellite positioning system using artificial satellites. In the GPS system, electric waves (GPS signal) are received from four artificial satellites (hereinafter, referred to as “GPS satellite”) among twenty four GPS satellites orbiting around the earth, a positional relation and a time error between a mobile object and the GPS satellites are measured on the basis of the received electric waves, and a position or an altitude of the mobile object on a map is calculated with high precision on the basis of triangulation.
Recently, the GPS is used for a car navigation system detecting a position of a driving automobile and comes into wide use. The car navigation device includes a GPS antenna for receiving a GPS signal, a processor for detecting a present position of a vehicle by processing the GPS signal received by the GPS antenna, a displayer for displaying the position detected by the processor on a map, and the like. A planar antenna such as a patch antenna is used as the GPS antenna.
A rod antenna (bar antenna) is known as a 3-wave sharing antenna capable of receiving a radio telephone band, an FM radio band, and an AM radio band. The bar antenna is used as the radio telephone antenna or the AM/FM radio antenna. The bar antenna is made of metal. A multi-frequency antenna capable of receiving 4 waves of the radio telephone band, the FM radio band, the AM radio band, and a GPS band was proposed (e.g., see Patent Document 1). In the multi-frequency antenna disclosed in Patent Document 1, since a matching board is disposed upright on the base and an antenna element is inclined to the perpendicular line, a GPS satellite has a low elevation angle. However, the low elevation angle of the GPS satellite does not have a bad influence on the GPS antenna.
In addition, there was proposed a complex antenna in which a patch antenna capable of receiving a circular-polarized wave from the GPS satellite or the like and a rod antenna capable of sending and receiving a linearly-polarized wave used in a mobile telephone or the like are disposed in parallel to be a unit (e.g., see Patent Document 2). In the complex antenna disclosed in Patent Document 2, a direction of the power feeding patch relative to the rod antenna is set so that the short axis is substantially perpendicular to a plane that includes an intersection point of the short axis and a long axis of the power feeding patch of the patch antenna and an axis line of the rod antenna. Accordingly, it is suppressed that the electric wave radiated from the rod antenna has a bad influence on the adjacent patch antenna.
Further, an antenna device which is capable of receiving an electric wave signal radiated from a satellite and a terrestrial wave signal radiated from a terrestrial antenna and is suitable for a vehicle was proposed (e.g., see Patent Document 3). In the antenna device disclosed in Patent Document 3, a planar antenna is provided upwardly on a surface of a board and, a base end of an antenna element including a helical antenna departs from the planar antenna laterally, and a front end of the antenna element is inclined by about 30° about the vertical direction in the departing direction.
There is provided a 3-wave sharing antenna device in which an AM/FM receiving antenna capable of an AM broadcasting wave and an FM broadcasting wave and a GPS receiving antenna capable of receiving a GPS broadcasting wave are integrated with each other (e.g., see Patent Document 4).
The SDARS (Satellite Digital Audio Radio Service) is a digital broadcasting service using a satellite (hereinafter, referred to as “SDARS satellite”) in the United States. That is, in the United States, a digital radio receiver receiving a satellite wave or a terrestrial wave from the SDARS satellite to provide digital radio broadcasting has been developed and put in practical use. Currently, in the United States, two broadcasting stations of XM and Sirius have provided radio programs more than total 250 channels throughout the whole country. The digital radio receiver is generally mounted in a mobile object such as an automobile, receives the electric wave in the frequency band of about 2.3 GHz, and provides the radio broadcasting. That is, the digital radio receiver is a radio receiver capable of providing the mobile broadcasting. Since the frequency of the reception electric wave is about 2.3 GHz, the reception wavelength (resonance wavelength) λ at that time is about 128.3 mm. The terrestrial wave is formed in the manner that the satellite wave is received by an earth station, the frequency of the received satellite wave is slightly shifted, and the wave is re-sent in a linearly-polarized wave. That is, the satellite wave is a circular-polarized wave, but the terrestrial wave is a linearly-polarized wave. In addition, the planar antenna such as the patch antenna is used as the SDARS antenna.
The antenna device for XM satellite radio receives the circular-polarized electric wave from two geostationary satellites, and receives the electric wave by using terrestrial linear-polarized equipments in a blind zone. On the other hand, the antenna device for Sirius satellite radio receives the circular-polarized electric wave from three orbiting satellites (synchro type), and receives the electric wave by the use of the terrestrial linear-polarized equipments in the blind zone.
Since the electric wave in the frequency band of about 2.3 GHz is used in such digital radio broadcasting, an antenna device receiving the electric wave is required to be installed outdoors. Accordingly, when the digital radio receiver is mounted in a mobile object such as an automobile, the antenna device is required to be mounted on the roof of the mobile object.
Patent Document 1: JP-A-10-93327
Patent Document 2: JP-A-2003-309411
Patent Document 3: JP-A-10-107542
Patent Document 4: JP-A-8-335824
As described above, various complex antenna devices including plural kinds of antennas are known. In addition to the 3-wave sharing antenna (bar antenna) as the complex antenna device, it is conceivable that a planar antenna such as an SDARS antenna and a GPS antenna is mounted on a main surface of an antenna base. That is, a complex antenna in which a planar antenna and a bar antenna are combined is conceivable. However, in such a complex antenna, a ripple increases due to directivity (horizontal-plane directivity) of the planar antenna by physical influence of the bar antenna made of metal. That is, deterioration in ripple performance occurs due to the low elevation-angle property of the planar antenna. In other words, the bar antenna made of metal acts as a metallic obstacle when viewed from the planar antenna.